The invention relates to a valve for controlling the flow of a hydraulic fluid, in particular for supplying a single-acting or double-acting consumer.
Such valves having pressure-compensated and non-pressure-compensated designs are known. Non-pressure-compensated valves make it possible to utilize the pressure differential between a high-pressure connection and a low-pressure connection of the valve in order to press a closing element against a valve seat. Therefore, these are also suitable for obtaining a secure seal even in the presence of high pressure differentials. Disadvantageously, however, the hydrostatic pressure differential acting on the closing element must be overcome in order to release the closing element from the valve seat. The force required to open the valve therefore increases as the pressure differential increases, and when such a valve is supposed to be actuated by means of an actuator, the actuator must be powerful enough to overcome the greatest pressure differential that can occur at the valve. Such actuators are naturally large and expensive.
A valve having a pressure-compensated design is known, for example, as the “WEDT-08” from Bosch-Rexroth. This conventional valve has a substantially cylindrical sleeve, in the case of which a first port is formed on an end face of the sleeve and a second port is formed on the circumferential surface thereof. A valve tappet, which can move in the valve sleeve, has an axial bore, via which the pressure of the first port is present at two end faces of the tappet that face away from each other. The hydrostatic pressure forces acting on the end faces of the tappet cancel each other out, and therefore, in order to switch the valve, only a slight actuating force is required by one of the actuators acting on the end face of the tappet remote from the first port.
However, the pressure-compensated design not only prevents high pressure at the first port from holding the tappet on the seat, but also prevents high pressure at the second port from releasing the tappet from the seat. If the aim is to use the valve in a hydraulic system in which the pressure at the second port can temporarily exceed the pressure at the first port and thereby endanger components of the system, a non-return valve must be installed in parallel in order to prevent such pressure peaks, which markedly increases costs and space requirements of a valve assembly for such an application. Such pressure peaks can occur, for example, on a self-propelled harvesting machine, when an assembly that is mounted so as to be displaceable by hydraulic cylinders, such as a front harvesting attachment, is exposed to external forces during use.